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The TCP/IP Guide

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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)
      9  TCP/IP Key Applications and Application Protocols
           9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)
                9  Usenet (Network News) and the TCP/IP Network News Transfer Protocol (NNTP)
                     9  TCP/IP Network News Transfer Protocol (NNTP)

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NNTP Overview and General Operation
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NNTP Client-Server Communication Process: News Posting and Access
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NNTP Inter-Server Communication Process: News Article Propagation
(Page 2 of 4)

Basic NNTP Propagation Methods

Now let's look at how messages are actually propagated between servers using NNTP. There are two techniques by which this can be done:

  • “Pushing” News: In the push model, as soon as a server receives a new message, it immediately tells its upstream and downstream neighbors about the message and asks them if they want a copy of it.

  • “Pulling” News: In the pull model, servers do not offer new articles to their neighbors. The neighboring servers must ask for a list of new messages if they want to see what has arrived since the last connection was established, and then request that the new messages be sent to them.

There are advantages and disadvantages to both of these techniques, but pushing is the model most commonly used today.

Key Concept: One important role that NNTP plays is its propagation of articles between Usenet servers, which is what makes the entire system possible. Two models are used for article propagation: the push model, in which a server that receives a new message offers it to connected servers immediately, and the pull model, where servers that receive new messages hold them until they are requested by other servers. The push model is usually preferred since it allows for quicker communication of messages around the system.



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NNTP Overview and General Operation
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NNTP Client-Server Communication Process: News Posting and Access
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